Comparing 6 and 10 sec exhalation time in exhaled nitric oxide measurements in children

Standard exhalation time for Fractional exhaled Nitric Oxide (FeNO) measurements is 10 sec but this is difficult for young children. Recommended exhalation time for children is 6 sec, but this was never substantiated in literature. We aimed to investigate the agreement between FeNO values measured with exhalation times of 6 and 10 sec and the preference of children for either method. The study population comprised children aged 5-17 years visiting the Pediatric Pulmonology outpatient clinic. FeNO values, measured during 6 (FeNO-6) and 10 (FeNO-10) sec (random order) using the single-breath online (SBOL) technique, were compared. Preferences for exhalation times were related to FVC values. Ninety-eight children (mean age 10.6 years) were included. Median FeNO-6 (15.2 ppb) and FeNO-10 (13.6 ppb) did not differ significantly (P = 0.259). Mean difference between FeNO-6 and FeNO-10 was -0.3 ppb, limits of agreement ranging from -5.8 ppb to +5.3 ppb. Sixty percent of children with a Forced Vital Capacity (FVC) less than 3 L preferred the FeNO-6 method. We found good agreement between FeNO-6 and FeNO-10, so they can be used interchangeably. An exhalation time of 6 sec was preferred by the majority of subjects with a FVC below 3 L.